This invention relates to a galvanized metal, typically steel, corrosion inhibitor concentrate comprising (a) an amine salt of a fatty acid or an amine salt of a derivative of a fatty acid, (b) preferably a salt of a non polymeric aromatic acid, and (c) preferably a nonionic or anionic surfactant, and water. The invention also relates to a process for inhibiting corrosion and/or stripping of galvanized steel subjected to acidic conditions, e.g. an amine citrate or citric acid cleaning solution.
Steel and other metals are often galvanized by electroplating a layer of a more active metal, e.g. zinc, on the surface of the base metal to make the metal more corrosion resistant. Galvanized steel is particularly useful in open circulating aqueous systems. Even though electroplating provides added protection to the metal against corrosion, the galvanized layer of the metal can degrade, corrode, or strip from the metal surface, particularly when the galvanized metal surfaces are exposed to acidic or sequestering solutions over time.
One common manner in which the galvanized coating is exposed to acids and/or sequesterants is during cleaning. The cleaners are used to remove corrosion products from the metal surfaces, e.g. iron oxide from corrosion. Often cleaning solutions which are acidic or moderately acidic are used to clean the metals found in open circulating aqueous systems. These cleaners often contain citric acid, amine citrates and/or other sequestering agents. There are established dosages for cleaners that vary for on-line and off-line cleaning applications. The dosages typically recommended are from 50 ppm to 10 percent (100,000) ppm. Although these cleaners are effective in removing corrosion products, they can cause the galvanized layer of the metal surface to strip from the metal surface after one or more cleanings.
Some corrosion inhibitors for galvanized surfaces are available, but they are normally functional under conditions of normal equipment service, not under the stressed conditions of chemical cleaning. European Patent Application EP 0 807 695 discloses a non-phosphorus corrosion inhibitor for industrial cooling water and airwasher systems. The corrosion inhibitor contains (1) a hydroxycarboxylic acid or water-soluble salt thereof, (2) a polyacrylate or water soluble salt thereof, and (3) a water-soluble polymer which acts as a dispersant. The corrosion inhibitor is used in aqueous solutions having a pH rangexe2x89xa77. On the other hand, U.S. Pat. No. 4,113,498 discloses a corrosion inhibitor for metal surfaces, which is the reaction product of an aliphatic carboxylic acid, a polyhydroxy carboxylic acid, and an alkanolamine. The corrosion inhibitor is used in aqueous solutions having a pH range of 7.5 to 10.0.
There is a need to develop a low-to-moderate pH corrosion inhibitor for zinc galvanized steel which can be used during the cleaning process without disrupting it. Such a corrosion inhibitor must be comprised of components that are environmentally acceptable. It must not appreciably interfere with the removal of corrosion products by the cleaner, and at the same time must protect the galvanized surface from attack by the cleaner.
This invention relates to a for galvanized metal, typically steel, corrosion inhibitor concentrate comprising:
(a) an amine salt of a fatty acid or an amine salt of a derivative of a fatty acid;
(b) preferably a salt of a non polymeric aromatic acid;
(c) preferably a nonionic or anionic surfactant having an HLB of 1 to 20; and
(d) water.
In contrast to the corrosion inhibitors of European Patent Application EP 0 807 695 A1 and U.S. Pat. No. 4,113,498, mentioned previously, which are typically used in aqueous solutions having a pH greater than 7.5, the subject corrosion inhibitor concentrate can be used in aqueous solutions having a lower pH, for instance such as from 2 to 8, preferably from 4.9 to 8, when used at the suggested dosage. A relatively small amount of the corrosion inhibitor protects galvanized steel from attack during the cleaning process, particularly from the amine citrate used in iron oxide cleaners. The corrosion inhibitor will inhibit corrosion and retard the stripping of galvanized layer on galvanized steel. It does this without adversely affecting the effectiveness of the cleaning solution. The components of the corrosion inhibitor do not create stress on the environment.
The invention also relates to a process for inhibiting corrosion and/or stripping of galvanized steel subjected to acidic conditions, e.g. an amine citrate or citric acid cleaning solution.
The amine salts of fatty acids or the amine salts of derivatives of fatty acids used in the concentrate are formed by neutralizing a carboxylic acid with an amine. The carboxylic acid used may be a saturated or unsaturated, mono-, di-, or polycarboxylic acid having a least six-carbon atoms per functional group. Specific examples include, but are not limited to, capric acid, lauric acid, and palmitic acid. Most preferably used as the carboxylic acid are higher fatty acids such as rosin acids, tall oil, and their derivatives, most preferably a C21 dicarboxylic acid. Other useful derivatives include partial esters of maleated tall oil fatty acid. The amine used to form the amine salt of a fatty acid or derivative thereof can be any primary, secondary, or tertiary aliphatic amine. Examples include alkylamines, for instance methylamine, ethylamine, propylamine, and butylamine; alkanolamines, for instance as monoethanolamine, diethanolamine, and triethanolamine; morpholine; and cyclohexylamine. Preferably, the amine is triethanolamine, or N, N-diethylethanolamine, dimethylamine, 1,2-diaminoethane, diaminopropane, ethanolamine, 2-methyl-2-amino-1-propanol, 5-aminopentanol, methoxypropylamine.
The amount of carboxylic acid and amine used to form the amine carboxylates can vary over wide ratios, but the amount typically used is such that the ratio of carboxyl groups of the carboxylic acid to amino groups of the amine is from 4:1 to 1:4, preferably about 2:1 to 1:2, most preferably about 1:1.
Although the amine salts can be used alone as corrosion inhibitors for galvanized metals, they are preferably used in combination with a salt of a non-polymeric aromatic acid. Preferably used as the salt of the non-polymeric aromatic acid are the alkali metal saltand of benzoic acid. The amount of salt of the non polymeric aromatic acid used is from 1:5 to 5: 1, parts by weight, 0.5:1 to 3:1 parts by weight based upon the total weight of the amine salt used, most preferably from 1:1 to 2:1.
Another optional, but preferred, component of the concentrate is a nonionic or anionic surfactant having hydrophilic-lipophilic balance (HLB) of 1-20. Preferably the surfactant is a polyoxyethylene-polyoxypropylene nonionic surfactant, having an average molecular weight of about 1000 to 10,000, preferably from 3000 to 5000, and a hydrophobe to hydrophile ratio of about 1:1 to 10:1, preferably from 3:1 to 10:1. The amount of nonionic surfactant use is from 1:30 to 2:1, preferably from 1:6 to 1:8. Other useful surfactants include linear alcohol ethoxylates, for example, one with 12 to 15 carbon atoms and 9 moles of ethoxylation; and alkali metal salts of fatty acids, for example, oleic acid.
Optional components include tolyltriazole, benzotriazole or the like for additional protection of yellow metals.
The corrosion inhibitor is most conveniently formulated as an aqueous solution of about 30 to 50 percent solids with a pH of about 7.3 to 7.8, preferably about 7.5. The aqueous solution may be added directly to the aqueous system containing the metal to be cleaned.
Typically the concentrate will contain from 5 to 30 parts by weight of amine salt, from 10 to 40 parts by weight of alkali benzoate, from 1 to 10 parts by weight of nonionic surfactant, and from 40 to 85 parts by weight of water, where said parts by weight is based upon the total weight of the concentrate. Preferably the concentrate will contain from 10 to 20 parts by weight of amine salt, from 20 to 40 parts by weight of alkali benzoate, from 1 to 5 parts by weight of nonionic surfactant, and from 50 to 70 parts by weight of water, where said parts by weight is based upon the total weight of the concentrate.
The dosage of the corrosion inhibitor used in the aqueous system varies over wide ranges and will depend upon a number of variables, for example whether the cleaning is off-line or on-line; the pH of the system treated; the type of cleaner being used; and the concentration of the cleaner being used. Typically the range will be on a solids basis from 20 ppm to 4000 ppm, more typically from 40 ppm to 3000 ppm, and most typically from 200 ppm to 2000 ppm. When used in a system cleaned off line by a moderate pH cleaner, the range will be from 500 ppm to 3000 ppm, preferably from 1000 ppm to 2000 ppm. When used in a system cleaned off-line by an acidic cleaner, the range will be from 1000 to 4000 ppm, preferably from 1000 to 3000 ppm.
When used in a system cleaned on-line by a moderate pH cleaner, the range will be from 20 to 300, preferably from 40 to 200 ppm. The corrosion inhibitor is particularly suited for aqueous systems having a pH of 2.5 to 8, particularly those containing a cleaner. After the cleaner and galvanized steel corrosion inhibitor are added to the aqueous system and allowed to operate, the aqueous system is usually flushed with water to remove cleaner and galvanized steel corrosion inhibitor and accumulated, dissolved corrosion products. Cleaning off-line generally takes about 24 hours to 14 days. Cleaning on-line generally takes several days to several weeks.